Wire electric discharge machining method and wire electric discharge machine utilizing pressurized gas for removing machining solution

ABSTRACT

A workpiece is machined by consecutively performing at least two of machining in a machining solution, machining in a mist and machining in a gas, such that at a point of time before the start of machining, except for the machining conducted in the machining solution, and a point of time after the operation of an automatic wire connecting device for conducting an automatic wire connection while the wire electrode is being held by a water column, the machining solution nozzles, can change from supplying the machining solution to supplying the pressurized gas. By the machining solution nozzles, liquid of the machining solution adhering to the workpiece and liquid adhering to the machining solution nozzle which is capable of dripping onto a face to be machined of the workpiece, are removed.

This application is a 371 of PCT/JP00/0660, filed Oct. 5, 2000.

1. Technical Field

The present invention relates to improvements in a wire electricdischarge machining method and a wire electric discharge machine inwhich electric power is supplied between a wire electrode and aworkpiece so that a workpiece is machined by electric discharge energygenerated between the wire electrode and the workpiece.

2. Background Art

Electric discharge machining has acquired a steadfast position as atechnique for machining metallic dies and others. Therefore, electricdischarge machining has been widely used for machining metallic dies inthe automobile industry, electric appliance industry and semiconductorindustry.

FIGS. 8A to 8E are schematic illustrations for explaining a mechanism ofelectric discharge machining. In the drawing, reference numeral 1 is anelectrode, reference numeral 2 is a workpiece, reference numeral 3 is anarc column, reference numeral 4 is a machining solution and referencenumeral 5 represents chips created in the process of electric dischargemachining. While the following processes (a) to (e), which correspond toFIGS. 8A to 8E, are being repeatedly conducted, removal machining isconducted on the workpiece 2 by electric discharge. Each processproceeds as follows.

(a) Formation of the arc column 3 by the generation of electricdischarge

(b) Local melt of the workpiece and vaporization of the machiningsolution 4 by the thermal energy of electric discharge

(c) Generation of vaporizing explosive power by the machining solution 4

(d) Dispersion of the melted portion (chips 5)

(e) Cooling, coagulation and restoration of insulation between theelectrodes executed by the machining solution

The present invention relates to wire electric discharge machining usedfor gouging, cutting and so forth. Concerning the technique of wireelectric discharge machining, there is a strong demand for higheraccuracy. For example, when metallic dies used in the field ofmanufacturing semiconductors, the dimensional accuracy of which is high,are machined, it is necessary to conduct machining with high accuracy of1 to 2 μm.

FIGS. 9A to 9C are schematic illustrations showing an example of thewire electric discharge machining process. In the drawing, referencenumeral 1 a is a wire electrode, reference numeral 2 is a workpiece,reference numeral 4 a is water which is a machining solution, andreference numeral 6 is an initial hole. FIG. 9A shows a first cutprocess which is a rough machining process, FIG. 9B shows a second cutprocess which is an intermediate finishing process to be conducted afterthe rough machining process, and FIG. 9C shows a third cut process whichis a final finishing process.

An example of the first cut process shown in FIG. 9A shows a gougingprocess in which the wire electrode 1 a is threaded into the initialhole 6 and the workpiece 2 is gouged by electric discharge. In the caseof the first cut process described above, since the surface roughnessand the accuracy are finished in the later process, it is unnecessary tomachine the workpiece with high accuracy, and it is important toincrease a rate of machining so as to enhance the productivity. In orderto enhance the rate of wire electric discharge machining, water 4 a isjetted out between the electrodes so that chips can be effectivelyejected from between the electrodes. In order to spray water 4 a betweenthe electrodes uniformly and prevent the breaking of the wire electrode1 a, a method is adopted in which water 4 a is stored up in a machiningtank and the workpiece 2 is dipped in the water 4 a. As described above,a means for supplying a machining solution between the electrodes isused.

In the conventional wire electric discharge machining method describedabove, the second cut process (shown in FIG. 9B), which is conductedafter the first cut process (shown in FIG. 9A), and the third cutprocess (shown in FIG. 9C), are conducted in the water 4 a which is amachining solution.

FIG. 10 is a view showing an example of the waveforms of voltage andcurrent between the electrodes. In the view, V is a voltage between theelectrodes, and I is a current between the electrodes, and t is time. Astate at time T1 in FIG. 10 shows that voltage is impressed between thewire electrode 1 a and the workpiece 2. When voltage is impressedbetween the electrodes, an attraction force acts between the positiveand the negative polarity. By this electrostatic force, the wireelectrode 1 a, the rigidity of which is low, is drawn onto the workpiece2 side, which could be a cause of vibration of the wire electrode 1 a.Due to the vibration, it becomes difficult to conduct electric dischargemachining with high accuracy.

A state at time T2 in FIG. 10 shows that vaporizing explosive power isgenerated in the machining solution by electric discharge energy (forexample, shown in FIG. 8C). The wire electrode 1 a is given a strongforce by the vaporizing explosive power created in the machiningsolution in a direction opposite to the workpiece 2, and vibration isgenerated. Due to the vibration, irregularities are caused on theprofile of the workpiece 2, which impairs the dimensional accuracy.

In the industry of semiconductors in which wire electric dischargemachining is utilized, the following cases are increased. For example,in the case of machining metallic dies of IC lead frames, very highaccuracy and very smooth surface roughness are required when a workpieceis machined, the dimensional accuracy of which is 1 μm, and the surfaceroughness of which is not more than 1 μm Rmax. In the case where highaccuracy and smooth surface roughness are required as described above,remarkable problems are caused by the aforementioned vibration of thewire electrode.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished to solve the above problems.It is an object of the present invention to provide a wire electricdischarge machining method and a wire electric discharge machinesuitable for conducting electric discharge machining with high accuracyand reliability.

The present invention provides a wire electric discharge machiningmethod in which electric discharge is generated between a wire electrodeand a workpiece so as to machine the workpiece by electric discharge,comprising the steps of: machining the workpiece while at least twotypes of machining in three types of machining including machining in amachining solution, machining in mist and machining in gas are beingcombined with each other; and removing at least one of the liquid of themachining solution adhering to the workpiece and the liquid of themachining solution having a possibility that the liquid drips onto amachining face of the workpiece at least at one of the point of timebefore the start of machining except for the machining conducted in themachining solution and the point of time after the operation of anautomatic wire connecting device for conducting an automatic wireconnection while the wire electrode is being held by a water column.

The present invention provides a wire electric discharge machine inwhich electric discharge is generated between a wire electrode and aworkpiece so as to machine the workpiece by electric discharge,comprising: at least one of the machining solution supply means forsupplying a machining solution between the electrodes and the mistsupply means for supplying mist between the electrodes; pressurized gasjetting means for removing at least one of the liquid of the machiningsolution adhering to the workpiece and the liquid of the machiningsolution having a possibility that the liquid drips onto a machiningface of the workpiece at least at one of the point of time before thestart of machining except for the machining conducted in the machiningsolution and the point of time after the operation of an automatic wireconnecting device for conducting an automatic wire connection while thewire electrode is being held by a water column; and positioning meansfor positioning by relatively moving the workpiece and the pressurizedgas jetting means.

Also, the present invention provides a wire electric discharge machinein which electric discharge is generated between a wire electrode and aworkpiece so as to machine the workpiece by electric discharge,comprising: at least two of the machining solution supply means forsupplying a machining solution between the electrodes, the mist supplymeans for supplying mist between the electrodes and the gas supply meansfor supplying gas between the electrodes; pressurized gas jetting meansfor removing at least one of the liquid of the machining solutionadhering to the workpiece and the liquid of the machining solutionhaving a possibility that the liquid drips onto a machining face of theworkpiece at least at one of the point of time before the start ofmachining except for the machining conducted in the machining solutionand the point of time after the operation of an automatic wireconnecting device for conducting an automatic wire connection while thewire electrode is being held by a water column; and positioning meansfor positioning by relatively moving the workpiece and the pressurizedgas jetting means.

Also, the present invention provides a wire electric discharge machinein which the pressurized gas jetting means is a machining solutionnozzle capable of changing over a fluid to be supplied between themachining solution and the pressurized gas.

Also, the present invention provides wire electric discharge machine inwhich a relative movement of the workpiece with the pressurized gasjetting means made by the positioning means is conducted according to aprogram for machining the workpiece.

The wire electric discharge machining method and wire electric dischargemachine of the present invention are composed as described above, and itis possible to combine the machining in a machining solution, themachining in mist and the machining in gas with each other, and furtherit is possible to utilize the essential characteristic of eachmachining. Therefore, it is possible to provide an effect that a highlyreliable wire electric discharge machining method and wire electricdischarge machine, which are appropriately used for machining with highaccuracy, can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are schematic illustrations showing an example of a wireelectric discharge machining method of an embodiment of the presentinvention.

FIG. 2 is a schematic illustration showing a state in which a machiningsolution has been ejected after the completion of rough machiningconducted in the machining solution.

FIG. 3 is a photograph of a workpiece taken after an automatic wireconnecting device has been operated.

FIG. 4 is an arrangement view showing a wire electric discharge machineof an embodiment of the present invention.

FIG. 5 is a view showing a structure of a machining solution nozzle.

FIGS. 6A to 6C are schematic illustrations showing a removing motion ofremoving a residual machining solution adhering to a workpiece by apressurized gas jetting means.

FIG. 7 is a schematic illustration showing a removing motion of removinga residual machining solution from an upper face of a workpiece by apressurized gas jetting means.

FIGS. 8A to 8E are schematic illustrations showing a mechanism ofelectric discharge machining.

FIGS. 9A to 9C are schematic illustrations showing a machining processof wire electric discharge machining.

FIG. 10 is a view showing an example of waveforms of voltage and currentimpressed between electrodes.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic illustration showing an example of a wire electricdischarge machining method of an embodiment of the present invention. Inthe drawing, reference numeral 1 a is a wire electrode, referencenumeral 2 is a workpiece, reference numeral 4 a is water which is amachining solution, reference numeral 6 is an initial hole, referencenumeral 7 is mist such as water and reference numeral 8 is gas such asair. FIG. 1A is a view showing a first cut process in which roughmachining is conducted, FIG. 1B is a view showing a second cut processin which intermediate machining is conducted after the rough machiningand FIG. 1C is a view showing a third cut process in which finalmachining is conducted. In this case, the first, the second and thethird cut process are expediently determined. Therefore, wire electricdischarge machining is not necessarily completed in the above threeprocesses. In the case where electric discharge machining is conductedwith low accuracy because the required accuracy is low, only the firstcut process is conducted or alternatively only the first and the secondcut process are conducted. In the case where the required accuracy ishigh, the cutting process is conducted by seven or eight times.

Next, an outline of the machining method will be explained below. In thefirst cut process shown in FIG. 1A, the wire electrode 1 a is threadedin the initial hole 6, and the workpiece 2 is gouged. In the first cutprocess, it is not required to conduct machining with such severesurface roughness and high dimensional accuracy because machining isconducted in the later process with severe surface roughness and highdimensional accuracy. Therefore, in the first cut process, it isimportant to increase a rate of machining so that the productivity canbe enhanced. In the same manner as that of the background art shown inFIGS. 9A to 9C, electric discharge machining is conducted while water 4a, which is a machining solution, is being interposed between theelectrodes by the machining solution supply means for supplying amachining solution between the electrodes. Concerning this machiningsolution supply means, at least either the means for dipping theworkpiece 2 in water 4 a in a machining tank or the means for jettingout water 4 a between the electrodes is used.

In the usual wire electric discharge machining, machining is continuedwhile the machining solution is being supplied between the electrodes bythe machining solution supply means even after the completion of thefirst cut process. However, as described in the background art, problemssuch as vibration of the wire electrode are caused in this case.Therefore, it is not appropriate for machining with high accuracy. Thepresent invention is characterized in that dimensional accuracy andsurface roughness are improved by conducting electric dischargemachining while a machining solution is not being interposed between theelectrodes in the finishing process.

In the second cut process shown in FIG. 1B which is an intermediatefinishing process, in order to improve the accuracy of a profile to bemachined by suppressing the occurrence of vibration of the wireelectrode 1 a, electric discharge machining is conducted not in themachining solution 4 a but in the mist 7. A rate of machining conductedin the mist 7 is by no means inferior to that conducted in the machiningsolution 4 a. Since the occurrence of vibration of the wire electrode 1a caused by an electrostatic force is suppressed, the machining accuracycan be enhanced. Electric discharge machining in the mist 7 can beconducted when the mist is jetted out between the wire electrode 1 a andthe workpiece 2, for example, by the mist supply means not shown.

In the third cut process shown in FIG. 1C which is the final finishingprocess, when electric discharge is conducted in the gas 8, theoccurrence of vibration of the wire electrode 1 a can be furthersuppressed. Machining in the gas 8 is conducted in the atmosphere.Alternatively, machining in the gas 8 is conducted when gas of apredetermined composition is jetted out between the wire electrode 1 aand the workpiece 2 by the gas supply means not shown.

The reason why it is possible to conduct electric discharge machiningwith high accuracy in the mist 7 or the gas 8 is described as follows.Since an intensity of the electrostatic force, which acts on the wireelectrode 1 a and the workpiece 2 when voltage is impressed between theelectrodes, is proportional to the dielectric constant between theelectrodes. Therefore, when the distances between the electrodes are thesame, the intensity of the electrostatic force in the case where themist 7 or gas 8 is interposed between the electrodes is one severaltenth of that in the case where the water 4 a is interposed between theelectrodes. (For example, the dielectric constant is the lowest invacuum and approximately 80 times as high as that in water.) Since thevaporizing explosive power caused by electric discharge is generated byliquid existing between the electrodes, when only the mist 7 or gas 8exists between the electrodes, the wire electrodes 1 a is seldomaffected by the vaporizing explosive power.

Accordingly, it is possible to conduct electric discharge machining withhigh accuracy in the mist 7 or gas 8. Therefore, when machiningconducted in the machining solution, machining conducted in the mist andmachining conducted in the gas are appropriately combined with eachother according to the productivity and the dimensional accuracyrequired for the workpiece, it is possible to satisfy the requiredspecification.

In the case where wire electric discharge machining is conducted whilemachining in the machining solution, machining in the mist and machiningin the gas are being combined with each other as described above,machining in the machining solution is changed over to machining in themist, machining in the machining solution is changed over to machiningin the gas, and machining in the mist is changed over to machining inthe gas.

FIG. 2 is a schematic illustration showing a state in which themachining solution has been ejected after the completion of roughmachining conducted in the machining solution. After this, electricdischarge machining is conducted in gas, which will be explained below.In FIG. 2, reference numeral 2 is a workpiece, reference numeral 4 b isa residual machining solution, reference numeral 9 is a surface plateand reference numeral 10 is a machining tank. The residual machiningsolution 4 b adheres onto an upper face and a face to be machined of theworkpiece 2. Even when electric discharge machining is conducted in gasunder the condition that the residual machining solution 4 b adheres tothe workpiece 2, it is impossible to provide the proper machiningcharacteristic of electric discharge conducted in gas. Therefore, it isnecessary to appropriately remove the residual machining solution 4 bwhich has adhered to the workpiece 2. Especially in the case of electricdischarge conducted in gas, even when a small quantity of residualsolution 4 b adheres to the workpiece 2, it is impossible to provide theoriginal machining characteristic in gas. Therefore, it is highlynecessary to remove the residual machining solution 4 b which hasadhered to the workpiece 2.

In FIG. 2, explanations are made into a case in which the residualmachining solution 4 b adheres to the workpiece 2. However, there is apossibility that the residual machining solution 4 b adhering to themachining solution nozzle, which is arranged in an upper portion of theworkpiece 2, drips onto a face to be machined of the workpiece 2 whichis being machined by electric discharge in gas. Therefore, it isnecessary to remove the residual machining solution 4 b not only fromthe workpiece 2 but also from the machining solution nozzle.

Also, in the case of changing over from the machining process conductedin the machining solution to the machining process conducted in themist, or also in the case of changing over from the machining processconducted in the mist to the machining process conducted in the gas, itis necessary to remove the machining solution adhering to the workpiece2.

In order to automatize wire electric discharge machining, an automaticwire connecting device is commonly used. This automatic wire connectingdevice operates in such a manner that water is jetted out in the processof connecting the wire electrode 1 a so as to hold the wire electrode 1a, the rigidity of which is low, by a water column, and the wireelectrode 1 a is automatically connected. This automatic wire connectingdevice is used when electric discharge machining is started from theinitial hole or when the breaking of the wire electrode la has happened.

FIG. 3 is a photograph of the workpiece taken after the completion ofoperation of the automatic wire connecting device. As can be seen inFIG. 3, water, which has jetted out in the automatic wire electrodeconnecting process, scatters and remains on an upper face of theworkpiece. Accordingly, it is necessary to remove water which hasadhered to the workpiece in the process of operation of the automaticwire connecting device.

FIG. 4 is an arrangement view showing a wire electric discharge machineof an embodiment of the present invention. In the drawing, referencenumeral 1 a is a wire electrode, reference numeral 2 is a workpiece,reference numeral 4 a is water which is a machining solution, referencenumeral 9 is a surface plate for fixing the workpiece 2, referencenumeral 11 is a wire bobbin, reference numeral 12 is a pressurized gas,reference numerals 13 a and 13 b are nozzles for jetting out a machiningsolution, reference numeral 14 is a capstan roller, reference numeral 15is a pinch roller, reference numeral 16 is an X table for driving theworkpiece 2 in the horizontal direction (X-direction), reference numeral17 is a Y table for driving the workpiece 2 in the horizontal direction(Y-direction), reference numeral 18 is an X-axis servo amplifier forcontrolling a drive motor not shown for driving the X-table 16,reference numeral 19 is a Y-axis servo amplifier for controlling a drivemotor not shown for driving the Y-table 17, reference numeral 20 is anautomatic wire connecting device, and reference numeral 21 is a controlmeans. The workpiece 2 is machined as follows. The wire electrode 1 a isheld and drawn by the capstan roller 14 and the pinch roller 15. Whilethe wire electrode 1 a is running, electric power for machining issupplied between the workpiece 2 and the wire electrode 1 a from anelectric power source not shown, and while the wire electrode 1 a andthe workpiece 2 are being relatively moved by the X-table and theY-table which are the positioning means, the workpiece 2 is machined byelectric discharge.

FIG. 5 is a view showing a structure of a machining solution nozzle. Themachining solution nozzle 13 a is taken as an example and explainedbelow. The structure and operation of the machining solution nozzle 13 bare the same as those of the machining solution nozzle 13 a. In FIG. 5,reference numeral 22 is a changeover means. Like reference charactersare used to indicate like parts in FIGS. 4 and 5. The changeover means22 is composed of, for example, an electromagnetic valve. When thischangeover means 22 is changed over by the control means 21 (shown inFIG. 4), the supply of water 4 a or the pressurized gas 12 to themachining solution nozzle 13 a can be changed over.

In the process of rough machining shown in FIG. 1A, the changeover means22 is changed over by the control means 21 so that the water 4 a can besupplied to the machining solution nozzle 13 a, and electric dischargemachining is conducted while the water 4 a is being supplied from themachining solution nozzle 13 a between the wire electrode la and theworkpiece 2.

Before the start of the intermediate finish machining process shown inFIG. 1B, the machining solution is ejected from the machining tank afterthe completion of rough machining shown in FIG. 1A, and the changeovermeans 22 is changed over by the control means 21 so that the pressurizedgas 12 can be supplied to the machining solution nozzle 13 a, and thepressurized gas 12 is jetted out from the machining solution nozzle 13a, so that the residual machining solution adhering to the workpiece 2can be removed, and at the same time the residual machining solutionadhering to the machining solution nozzle arranged in an upper portionof the workpiece 2 can be removed.

In the same manner, before the start of the final finishing processshown in FIG. 1C, the pressurized gas 12 is jetted out from themachining solution nozzle 13 a, and liquid which has adhered to theworkpiece 2 by the deposition of the mist 7 is removed and also liquidwhich has adhered to the machining solution nozzle arranged in an upperportion of the workpiece 2 is removed.

As described above, as a pressurized gas jetting means for removing theresidual machining solution, the pressurized gas 12 is supplied to themachining solution nozzles 13 a and 13 b, and the pressurized gas 12 isjetted out from these machining solution nozzles 13 a and 13 b. In thisway, the residual machining solution adhering to the workpiece 2 can beeffectively removed and also the residual machining solution adhering tothe machining solution nozzle arranged in an upper portion of theworkpiece 2 can be effectively removed. For example, when thepressurized gas 12 is jetted out from the machining solution nozzle 13a, the residual machining solution adhering to the workpiece 2 can beremoved and also liquid adhering inside the machining solution nozzle 13a can be removed. When the pressurized gas 12 is jetted out from themachining solution nozzle 13 b, the residual machining solution adheringto the periphery of the machining solution nozzle 13 a, the residualmachining solution having a possibility of dripping onto a face to bemachine of the workpiece 2, can be removed.

Accordingly, deterioration of the machining characteristic caused by theresidual machining solution adhering to the workpiece 2 can beeffectively suppressed, and also deterioration of the machiningcharacteristic caused by dripping of the residual machining solutionadhering to the machining solution nozzle arranged in an upper portionof the workpiece 2 can be effectively suppressed. As a result, it ispossible to conduct machining with high reliability.

The pressurized gas jetting means for removing the residual machiningsolution is not limited to the structure shown in FIG. 5 in which thepressurized gas is jetted out from the machining solution nozzle. It ispossible to provide the pressurized gas jetting means separately fromthe machining solution nozzle.

When a gas supply means for jetting out gas of a predeterminedcomposition between the wire electrode 1 a and the workpiece 2 is usedin the electric discharge machining conducted in gas as shown in FIG.1C, the gas supply means can be also used for the pressurized gasjetting means for removing the residual machining solution.

FIGS. 6A to 6C are schematic illustrations showing a removing motion ofremoving a residual machining solution adhering to a workpiece by apressurized gas jetting means. In this case, the machining solutionnozzle is used for the pressurized gas jetting means. In FIGS. 6A to 6C,reference numeral 1 a is a wire electrode, reference numeral 2 is aworkpiece and reference numeral 13 a is a machining solution nozzle usedfor the pressurized gas jetting means. The machining solution nozzle 13a and the workpiece 2 can be relatively moved with each other, forexample, by the positioning means composed of the X table 16 and the Ytable 17 shown in FIG. 4.

The residual machining solution adhering to an upper face of theworkpiece 2 can be removed as follows. As shown in FIG. 6A, after thecompletion of rough machining which is conducted in the machiningsolution, while giving a step movement corresponding to the diameter ofthe machining solution nozzle 13 a as shown in FIG. 6B, the machiningsolution nozzle 13 a and the workpiece 2 are moved relatively with eachother by the positioning means so that the machining solution nozzle 13a can conduct scanning on the entire upper face of the workpiece 2, andthe pressurized gas 12 is jetted out from the machining solution nozzle13 a. In this way, the residual machining solution adhering to the upperface of the workpiece 2 can be removed. Next, as shown in FIG. 6C, themachining solution nozzle 13 a and the workpiece 2 are relatively movedwith each other so that the machining solution nozzle 13 a can followthe locus of machining, and the pressurized gas 12 is jetted out fromthe machining solution nozzle 13 a. In this way, the residual machiningsolution adhering to the face to be machined can be removed. When thepressurized gas 12 is jetted out from the machining solution nozzle 13 aas described above, the residual machining solution adhering inside themachining solution nozzle 13 a can be simultaneously removed.

The residual machining solution adhering to the periphery of themachining solution nozzle 13 a, the residual machining solution having apossibility of dripping onto a face to be machine of the workpiece 2,can be removed in the same manner when the pressurized gas 12 is jettedout from the machining solution nozzle 13 b.

In the case where the automatic wire connecting device 20 shown in FIG.4 is operated, water adhering to the workpiece 2 as shown in FIG. 3 canbe removed in the same manner when the pressurized gas 12 is jetted outfrom the machining solution nozzle 13 a.

After the residual machining solution adhering to the upper face andalso adhering to the face to be machined of the workpiece 2 has beenremoved by the method described above and also after the residualmachining solution adhering to the machining solution nozzle arranged inan upper portion of the workpiece 2, the residual machining solutionhaving a possibility of dripping onto the face to be machined of theworkpiece 2, has been removed by the method described above, electricdischarge in mist or electric discharge in gas is conducted on theworkpiece 2. Due to the foregoing, the original machining characteristiccan be provided.

In the above explanations, the residual machining solution on the upperface of the workpiece 2 is removed when the machining solution nozzle 13a, which is a pressurized gas jetting means, is made to conduct scanningon the entire upper face of the workpiece 2 as shown in FIG. 6B. Insteadof that, the machining solution nozzle 13 a, which is a pressurized gasjetting means, may be moved relatively with the workpiece 2 while aquantity of offset is being changed according to the machining programby which the workpiece 2 has been machined as shown in FIG. 7.

When the above machining program is used, the residual machiningsolution can be effectively removed in a short period of time.Accordingly, it is possible to reduce waste time in the process ofmachining. Therefore, the productivity can be enhanced.

INDUSTRIAL APPLICABILITY

As described above, the wire electric discharge machining method of thepresent invention can be appropriately used for a highly accurateelectric discharge machining work.

What is claimed is:
 1. A wire electric discharge machining method inwhich electric discharge is generated between a wire electrode and aworkpiece so as to machine the workpiece by electric discharge,comprising the steps of: machining the workpiece by performing at leasttwo types of machining including machining in a machining solution,machining in a mist and machining in a gas; and removing at least one ofthe liquid of the machining solution adhering to the workpiece and theliquid of the machining solution capable of dripping onto a machiningface of the workpiece, wherein the step of removing is performed atleast at one of before the start of machining, except for the machiningconducted in the machining solution, and after the operation of anautomatic wire connecting device for conducting an automatic wireconnection wherein the wire electrode is being held by a water column.2. The wire electric discharge machining method according to claim 1,wherein the operation of the automatic wire connecting device occursbefore performing at least one of machining in the mist and machining inthe gas.
 3. A wire electric discharge machine in which electricdischarge is generated between a wire electrode and a workpiece so as tomachine the workpiece by electric discharge, comprising: at least one ofmachining solution supply means for supplying a machining solutionbetween the electrodes and mist supply means for supplying a mistbetween the electrodes; pressurized gas jetting means for removing atleast one of the liquid of the machining solution adhering to theworkpiece and the liquid of the machining solution capable of drippingonto a machining face of the workpiece, at least at one of before thestart of machining, except for the machining conducted in the machiningsolution, and after the operation of an automatic wire connecting devicefor conducting an automatic wire connection wherein the wire electrodeis being held by a water column; and positioning means for positioningby relatively moving the workpiece and the pressurized gas jettingmeans.
 4. A wire electric discharge machine in which electric dischargeis generated between a wire electrode and a workpiece so as to machinethe workpiece by electric discharge, comprising: at least two ofmachining solution supply means for supplying a machining solutionbetween the electrodes, mist supply means for supplying a mist betweenthe electrodes and gas supply means for supplying a gas between theelectrodes; pressurized gas jetting means for removing at least one ofthe liquid of the machining solution adhering to the workpiece and theliquid of the machining solution capable of dripping onto a machiningface of the workpiece at least at one of before the start of machining,except for the machining conducted in the machining solution, and afterthe operation of an automatic wire connecting device for conducting anautomatic wire connection wherein the wire electrode is being held by awater column; and positioning means for positioning by relatively movingthe workpiece and the pressurized gas jetting means.
 5. A wire electricdischarge machine according to claim 3, or 4, wherein the pressurizedgas jetting means is a machining solution nozzle capable of changingbetween supplying the machining solution and supplying the pressurizedgas.
 6. A wire electric discharge machine according to claim 3, or 4,wherein a relative movement of the workpiece with the pressurized gasjetting means made by the positioning means is conducted according to aprogram for machining the workpiece.
 7. The wire electric dischargemachine according to claim 3 or 4, wherein the operation of theautomatic wire connecting device occurs before performing at least oneof machining in the mist and machining in the gas.